The present invention relates to a process for the production of pulped cellulose material, in particular wood fibers, up to a fiber length of 20 mm, with a high proportion of thermocurable resin. The coated wood fibers are suitable for the production of decorative moldings, where they are initially shaped to form a fiber mat and then compressed at high temperature.
The process according to the present invention proceeds from known processes in which wood chippings are initially softened using steam and subsequently comminuted, for example, between two grinding disks, to form wood fibers having a length of up to 20 mm. An aqueous alkaline solution of a thermocurable resin is then applied to the moist wood fibers, and the coated wood fibers are dried, for example, using hot air, to a residual moisture, content of less than 15% by weight (see U.S. Pat. No. 4,503,115). When carrying out this known process, however, there is the danger of the resincoated particles sticking to the drying tube wall during drying and, in an extreme case, blocking the drying tube, which can easily cause autoignition.
It is also known to transport the wood fibers after the pulping station in a steam/air stream, to remove the major part of the steam stream from the wood fibers before applying the resin, to apply the aqueous resin solution to the fiber particles carried by the residual steam stream in a blow plant, and then to dry the coated wood fibers (see German Offenlegungsschrift No. 3,609,506). Although this process has the advantage that relatively little energy is necessary during drying, due to the previously reduced proportion of steam, there is a danger in this process of the resin solution mixing insufficiently with the wood fibers and of undesired pre-compression occurring, which can cause problems during further processing of the coated wood fibers.
For example, poor mixing of wood fibers with the resin can result in the formation, by drying resin drops, of glue nests in the finished board. These nests result in undesired reductions in the optical and technical quality. These disadvantages of the known process are particularly serious if relatively large amounts of resin, relative to the amount of wood fibers, are to be employed, as is disclosed, for example, in U.S. Pat. No. 4,503,115. A further disadvantage is that, with the use of large amounts of resin in accordance with the aforesaid patent, the line labeled 28 in the figure of Offenlegungsschrift No. 3,609,506 would become blocked with resin and fiber particles.